Usually, in electrically-powered automobiles, fuel-cell vehicles, hybrid electric motorbikes, and other electrically-powered vehicles, the high-voltage circuit connected to the high-voltage battery and the vehicle electric circuit grounded to the vehicle chassis are isolated. The ground fault detector described in Japanese Kokai Patent Application No. 2003-250201 is an example of a grounding fault detector that determines whether the high-voltage power source is grounded.
In this ground fault detector, one side of a coupling capacitor is connected to the plus terminal of a DC power source, and a square-wave pulse signal at a prescribed frequency is applied to the measurement point on the other side of the coupling capacitor. The occurrence of ground faults in the DC power source can be detected by the voltage generated at the measurement point.
Although the known ground fault detector can detect the occurrence of a ground fault, it cannot determine its cause. Ground faults may occur, for example, due to the direct contact of the high-voltage circuit that includes the power source harness to the vehicle chassis, or to the presence of water that has penetrated between the high-voltage circuit and the vehicle chassis. Since the cause of a ground fault is not identified, repair becomes difficult.